Light dictionary: The most important basic parameters of lighting technology


Luminous flux, luminous intensity, light color – the basic parameters of lighting technology are often associated with big question marks. We bring light into the dark and clarify the most important terms.

Luminous flux

Luminous flux is the amount of light that is emitted by a light source. The emitted light output is given in the unit lumen (lm). The so-called luminous efficacy is used as a measure of the efficiency of a light source – the ratio of the luminous flux to the electrical power consumed (lm / W).

Abbreviation Φ Phi

Unit of measurement lm (lumens)

Luminous intensity

A light source emits its luminous flux to different degrees in individual directions. The luminous intensity comprises the luminous flux emitted in a certain direction. Reflectors or other elements that direct the light significantly influence the intensity of the light intensity. The light intensity distribution of a light source can be approximately calculated using a computer simulation and displayed using a light intensity distribution curve (LVK).

Abbreviation Ι

Unit of measurement cd (candela)


Illuminance is the amount of luminous flux that strikes any surface. For example, a candle flame has an illuminance of approximately 1 lux at a distance of one meter. The required illuminance for e.g. Work surfaces are recorded in the relevant standards (e.g. EN 12464 “Lighting of workplaces”).

Abbreviation E

Unit of measurement lx (lux)

Calculation E (lx) = luminous flux (lm) / area (m2)


Luminance is the only basic parameter in terms of lighting technology that can be perceived by the human eye. It describes the ratio of the emitted light intensity to the size of the illuminated surface and depends strongly on the reflectance of e.g. Colors or surfaces.

Abbreviation L

Unit of measurement cd / m2

Light color

The light color, also called color temperature, determines the color appearance of the light. The warm white light of the HOLY TRINITY design lights has a slightly reddish color with a color temperature of 3000 Kelvin, while daylight white light has a bluish color with over 5300 Kelvin. Universal or neutral white light lies exactly in between with a color temperature of 3,300 to 5,300 Kelvin. While the light color is not a decisive criterion for conventional light bulbs, it is definitely relevant when buying an LED light. Depending on the model, the light color can influence not only the basic mood of the room, but also the human biorhythm.

Unit of measurement K (Kelvin)

Color rendering

Color rendering describes the ability of a light source to reproduce surface colors as true to color as possible compared to a reference light source. It is characterized by the color rendering index Ra (CRI for Color Rendering Index). A CRI of 100 stands for the best color rendering; A CRI of at least 80 (good color rendering) is recommended at workplaces.

Quality characteristics of light

In order to guarantee ‘good light’, various quality characteristics must be taken into account in the exterior and interior lighting. All in all, the individual components of the lighting quality ensure optimal lighting quality. In addition to the classic criteria such as the lighting level or the brightness distribution, the lighting quality features now also include components such as energy efficiency or the possibility of using light as a room design element.

We will provide you with an overview of all relevant quality features in one of our upcoming articles. Subscribe to our newsletter so you don’t miss anything.

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